A variety of implantable medical devices (IMDs) are used for chronic, i.e., long-term, delivery of therapy or diagnostic monitoring to patients suffering from a variety of conditions, such as cardiac dysfunction, chronic pain, tremor, Parkinson's disease, epilepsy, urinary or fecal incontinence, sexual dysfunction, obesity, spasticity, or gastroparesis. As examples, electrical stimulation generators are used for chronic delivery of electrical stimulation therapies such as cardiac pacing, cardiac cardioversion/defibrillation, neurostimulation, muscle stimulation, or the like. Pumps or other fluid delivery devices may be used for chronic delivery of therapeutic fluids, such as drugs, proteins, growth factors, pain relief agents or genetic agents. Typically, such devices provide therapy continuously or periodically according to parameters contained within a program. A program may comprise respective values for each of a plurality of parameters, specified by a clinician. The devices may receive the program from a programmer controlled by the clinician.
Examples of such implantable medical devices include implantable fluid delivery devices, implantable neurostimulators, implantable cardioverters, implantable cardiac pacemakers, implantable cardioverter-defibrillators, and cochlear implants. Typically, such devices are implanted in a patient to deliver therapy to or measure a signal from a target site within the patient under specified conditions on a recurring basis.
For example, an implantable fluid delivery device may be implanted at a location in the body of a patient and deliver a fluid medication through a catheter to a selected delivery site in the body. Similarly, an implantable electrical stimulator can be implanted to deliver electrical stimulation therapy to a patient at a selected site. For example, an implantable electrical stimulator delivers electrical therapy to a target tissue site within a patient with the aid of one or more medical leads that include electrodes. An electrical stimulator may deliver therapy to a patient via selected combinations of electrodes.
Precise placement of a lead or catheter, or at least knowledge of positioning of the lead or catheter, may be helpful in programming and delivering therapy. As one example, knowledge of the positions of electrodes carried by one or more leads may be helpful in formulating efficacious therapy, both upon implantation and over the course of therapy following implantation. As another example, the position of the distal outlet of a catheter may be helpful in determining proximity to a therapeutic target, both upon implantation and over the course of therapy following implantation. Knowledge of the location of a device element may further aid in the interpretation of sensed physiologic data.